1. Field of the Invention
The present invention relates to an electrode terminal connection structure for connecting a non-insulated semiconductor module to a dual inverter structure used in the motor control apparatus for industrial vehicles.
2. Description of the Prior Art
Conventionally, a semiconductor module with a large current capacity is used as the switching device of an inverter directly supplying a main motor with electric power in a motor control apparatus used in battery-powered vehicles, such as a battery forklift, etc. A semiconductor module is obtained by incorporating a plurality of power semiconductor chips into one insulated package, and there are modules with a variety of internal compositions, such as a module in which the current capacity is increased by simply incorporating chips of the same kind in parallel, a module in which a simple circuit is composed of a plurality of kinds of chips, a module in which a drive circuit composed of semiconductor chips is embedded, etc. Usually the package is made of plastic, and the concavity inside the package is filled with a gel and epoxy insulating agent from the bottom to prevent a chip peripheral circuit from oxidizing.
Since a semiconductor module is used to control a large current, a semiconductor module generates a lot of heat. For this reason, a non-insulated type is generally used in which semiconductor chips, being the current control circuit of a heat source, are directly mounted on a heat-radiating substrate with both a high thermal capacity and a high heat-radiation efficiency (highly heat-conductive) and in which the heat-radiating substrate itself is used as one electrode. Usually the heat-radiating substrate of a semiconductor module having such a structure is provided with a heat sink made of aluminum, etc., and is highly heat-conductive as a heat-radiating material to improve the radiation efficiency, which also serves to secure the semiconductor module itself.
A switching frequency usually used in a semiconductor module structured in this way, for example, in the above-described battery vehicle, is approximately 10 kHz.
When a semiconductor module structured as described above is actually used at the above-described switching frequency, the occurrence of a large inductance in the wiring of an internal circuit and the wiring connecting the semiconductor module to the outside cannot be avoided, and the occurrence of a large inductance causes a fairly large loss of switching power (hereinafter called a xe2x80x9cswitching lossxe2x80x9d) when a switching element is turned off. When the switching element is turned off, a fairly large surge voltage also occurs, which electrically damages the internal circuit.
This switching loss is an electric power loss occurring inside the semiconductor module when a device with a control electrode like the above-described semiconductor switch performs switching, and since usually many (5 or 6) semiconductor switches are used in the above-described motor control apparatus, the total switching loss occurring in these switches becomes a serious problem. This large loss, for example, greatly affects the drive and operation of the above-described battery vehicle, etc., and thermally damages the semiconductor switches since the lost electric power is converted into heat.
Conventionally, the reduction of the wiring inductance, that is, the reduction of both the switching loss and surge voltage has been realized by arranging two pieces of electrode wiring for the main current (for example, in the case of a MOS FET, source electrode wiring and drain electrode wiring) through which a large current flows in and out of the semiconductor module in opposite directions as input and output, in parallel and as close as possible to each other as much as possible and by causing an electro-magnetic effect which offsets (cancels) the two pieces of wiring inductance due to a reciprocal induction function.
FIG. 1 is the circuit diagram of an inverter used in the above-described semiconductor module, and each of the switching elements Q1 through Q6 shown in FIG. 1 correspond to one semiconductor module.
Then, the rotation of a three-phase motor M can be controlled by inputting a control signal from a drive circuit, which is not shown in FIG. 1, to the gate electrode of each switching element (semiconductor module).
Two of the above-described inverters, that is, one for driving and the other for lifting are needed in industrial vehicles, such as a battery-powered forklift, etc. Recently, a dual inverter structure 1 in which a small size, light weight and low cost can be realized by arranging two inverters 2 and 3 in parallel, making the inverters share common power capacitors, bus electrodes, etc., and thereby realizing a single module, as shown in FIGS. 2A and 2B (2A and 2B are a top view and side view, respectively), is proposed.
FIG. 3 is a side view in which the conventional connection structure of a pair of modules corresponding to a pair of upper and lower arms in the case where Q1 and Q2 shown in the circuit diagram (FIG. 1) are paired, are extracted and enlarged. Since the current flowing in the circuit is relatively small and thereby gate electrodes are not affected much by the wiring inductance, the gate electrodes are omitted in FIG. 3.
As shown in FIG. 3, the semiconductor modules used have a non-insulated structure in which base substrates 6a and 6b are also used as drain electrodes and in which source electrodes 7a and 7b are vertically installed along the inner sides of packages 8a and 8b from the joint part mounted on the upper surfaces of package 8a and 8b, as shown in dotted lines.
The semiconductor module has a sandwich structure in which a sufficiently thin insulation sheet 9 is inserted. The two extensions of a positive electrode 10 beneath the lower surface and a negative electrode 11 of a bus electrode plate 5 located above inverters 2 and 3 are used as a positive electrode terminal 12 and a negative electrode terminal 13, respectively, are extended to the drain electrode 6a of the Q1 module and the source electrode 7b of the Q2 module, respectively, and are connected and secured using screws 14.
The source electrode 7a of the Q1 module and the drain electrode 6b are connected using an inter-electrode terminal 15 made of copper plate, and a part of the terminal constitutes the output part to a drive motor M.
The positive electrode terminal 12 is divided into two parts in the longitudinal direction, and the inter-module electrode terminal 15 is positioned between the divided terminals.
However, according to the conventional semiconductor module connection structure in the above-described dual inverter structure 1, the electrode terminals 12, 13 and 15 connected to each semiconductor module correspond to the two extensions of the electrode plates 10 and 11 of the bus electrode plate 5 and a single copper plate, respectively, and as shown as D in FIG. 3, gaps are provided between the packages 8a and 8b in order to make tools, such as a driver, etc., easy to access if they are secured with screws 14, and the source electrodes 7a and 7b inside the packages 8a and 8b of the semiconductor module and the vertical portions of the electrode terminals 12 and 15, respectively, are separated and geometrically parallel. For this reason, the offset effect of the wiring inductance due to the reciprocal induction function in the vertical portions cannot be expected and thereby both surge voltage and switching loss are proportional.
Since many electrolytic capacitors are mounted as power capacitors 4 on the bus electrode plate 5, the weight of the semiconductor module becomes large, and thereby according to the conventional structure, reinforcing materials, such as a bracket 16, etc., must be installed in order to support the bus electrode plate 5 above the entire circuit.
An object of the present invention is to provide an electrode structure of a semiconductor module such that both surge voltage and switching loss can be greatly reduced by realizing a dual inverter structure in which there is no need to install reinforcing materials, such as a bracket, etc., when a semiconductor module is connected to the dual inverter structure and in which the offset of wiring inductance due to a reciprocal induction function can be realized even both in the side of the source electrode inside a package and in the vertical portion of an electrode terminal inside a package.
Although the present invention aims to solve the problem of a semiconductor switch consisting of MOS FETS, the present invention is not limited to this, but can also be applied to other semiconductor switches consisting of bipolar transistors, thyristors, etc., which have the same problem as the semiconductor switch consisting of MOS FETs. Since the description of the respective electrode varies depending on the kind of semiconductor switch, for simplicity a main current input electrode, a main current output electrode and a control electrode are used here taking into consideration the function of the electrodes.
For example, in the case of a semiconductor switch consisting of MOD FETs, a drain electrode, a source electrode and a gate electrode correspond to the main current input electrode, the main current output electrode and the control electrode, respectively.
In order to solve the above-described problem, first the present invention is applied to an electrode terminal connection structure connecting a non-insulated semiconductor module in which a conductive base substrate is also used as a main current input electrode, to a dual inverter structure. The present invention has a structure in which electrode terminals for inputting the main current from outside the semiconductor module to the base substrate as the main current input electrode are vertically installed on the base substrate in such a way that the electrode terminals are parallel with and close to a main current output electrode vertically installed inside the package of the semiconductor module, for which the current flows in opposite directions through the portions closely located and parallel to the source electrode and the electrode terminal.
Thus, wiring inductance is offset due to a reciprocal induction function even between the source electrode inside a package and the vertical portion of an electrode terminal, and a great reduction in both surge voltage and switching loss can be realized.
According to the present invention, both the more secure vertical mounting of electrode terminals and the support of a bus electrode plate can be realized by forming a block of an electrode terminal in a block shape, and thereby both the simplification and light weight of the entire dual inverter structure can be realized.
The electrode terminals formed in a block shape can be secured to the base substrate with screws passing through the base substrate from the top.
Thus, the gap provided between the inner side of a package along which a source electrode is vertically installed and an electrode terminal in the conventional structure can be eliminated, the source electrode inside the package and the electrode terminal can be located parallel and close to each other and thereby the wiring inductance offset effect due to the reciprocal induction function can be utilized by passing current in opposite directions through the source electrode and the electrode terminal.